Composite solid propellants commonly comprise one or more solid inorganic or organic oxidizer materials uniformly dispersed in a matrix of plastic, resinous or elastomeric material. The matrix, also known as the "binder", provides fuel for the combustion of the propellant. While the oxidizer material generally comprises the major constituent of the composite solid propellant, such propellants often contain (in addition to the binder) fuels, such as metal powders, and solid and/or liquid additives to enhance the ballistic and/or physical performance of the propellant.
In some applications, it is desirable to reduce the burning rate of the composite solid propellant. For example, the thrust provided by the burning propellant can be provided, for a given amount of propellant, over a longer period of time with a relatively slow burning propellant than with one which burns at a comparatively rapid rate, i.e. the given amount of propellant will be consumed faster at the high burning rate than at the reduced burning rate. Unfortunately, achieving these reduced burning rates without sacrificing other properties of the composite solid propellant, such as its specific impulse or efficiency of fuel combustion, has been difficult if not impossible. Particularly in the case of composite solid propellants which employ ammonium perchlorate (AP) as the oxidizer, attempts to reduce the burning rate of the propellant while maintaining its other properties have met with limited success.
Generally, the methods employed for reducing the burning rate of AP-containing composite solid propellants which do not result in a reduction in specific impulse have been limited to the use of large particle size AP. However, there is a limit to the larger AP size which can be employed in the composite solid propellant and still obtain efficient combustion of the metal powder fuels which are commonly utilized in such propellants. The burning rate of AP-containing composite solid propellants has also been reduced by increasing the binder content of the propellant, but this causes a significant decrease in both propellant density and fuel combustion efficiency. Increasing the metal fuel content likewise reduces the burning rate, but reduces the fuel combustion efficiency. Finally, many additives have proven to reduce the burning rate of AP-containing composite solid propellants, but usually specific impulse, fuel combustion efficiency or both must be sacrificed.